About 7 percent of the voters in the open GOP primary were Democrats and 28 percent were independents, according to exit polls published by MSNBC.

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Both figures mark a huge uptick from 2008. That year, Democrats made up just 3 percent of the Ohio GOP primary electorate and independents made up 17 percent.

It remains to be seen which of the Republican candidates will benefit from the uptick in participation.

Trump has touted his ability to bring new voters into the Republican fold, raising the possibility that he will score a win in the state.

But those new voters also might be seeking to block the real estate mogul. If so, the big beneficiary could be Kasich, who has been running neck and neck with Trump in the state and enjoys high favorability ratings there.

Matt Borges, the Ohio Republican Party chairman, told MSNBC that he believes many Democrats are flocking to Kasich, who performed well with Democrats when winning his first term as governor.

"Democrats obviously understand John Kasich's crossover appeal and many of them are crossing over in the Republican primary [to vote for him]," said Borges, who has endorsed Kasich.

Ohio is likely make-or-break for Kasich, who has yet to win a contest so far.